Limited resources of energy despite the exponentially increasing amount of its demand have forced researchers to explore and use renewable resources of energies, for example, wind energy, solar energy, etc. Among those that convert nature inspired energy to electrical energy, piezoelectric beams, which turn ambient mechanical vibrations into electrical power, are also of great interest. There exist several commercially available devices that are able to convert mechanical pressure into an electric signal, for example, Seiko Kinetic watch, mechanical wind up radios, piezoelectric igniter, etc.
The word ‘piezo’ is derived from the Greek word for pressure. The piezoelectric effect was discovered in 1880 in an attempt to find out how pressure will turn into electricity. It was noticed when pressure is applied to a quartz crystal, this component acts as an energy transfer function between mechanical and electrical energies. However, later it was found the inverse piezoelectricity effect as an externally applied electrical field was seen to cause deformation in the crystal. This effect greatly contributed to the development of submarine sonars during World War I. The advent of piezoelectric stacks invited a great and growing interest into the subject, so that over a few decades, new piezoelectric materials and applications were developed. Initially, these materials were mostly used as transducers and sensors as they did not have enough energy in the output signal.
In the context of harvesting energy from a vehicle tire, conventionally, piezoelectric beams were placed on the inner surface of a vehicle's tire for energy harvesting. In the case of inner surface attachment, the strain applied to the piezoelectric material is low. This structure had low efficiency and was not feasible for industrial applications. Alternately, piezoelectric beams were positioned on the outer surface of vehicle tire for energy harvesting purpose. This attempted to compensate the low efficiency of piezoelectric beams attached to the inner surface of a vehicle's tire. However, in the case of outer attachment, the piezoelectric stack is damaged and deformed easily. As such, there is a need in the art for a piezoelectric energy harvesting system, which converts energy efficiently and is not damaged or deformed easily.
Additionally, there has not been any approach to transmit the harvested electrical power to the battery with low loss, as it is impossible to connect the harvester unit to the storage battery with a simple conductive wire directly. The reason is that the system power supply, that are tires, are rotating, while the storage unit, that is battery, is fixed in its place. Hence, such a direct wire connection will cause hard twists in the wire around itself and results in the system failure immediately. Traditionally, wireless energy transmission with simple coils and electromagnetic rules to get rid of wires have been suggested. However, the efficiency of wireless transmission is very low and yields to high rate of loss in the system. At least for this reason, there is no commercialized wireless-powered device in a car, whose source of energy is piezoelectric beams mounted in the tire.
Hence, Applicants have identified that there is a long felt, but unresolved need for a piezoelectric energy harvesting system, which converts energy efficiently and is not damaged or deformed easily. Furthermore, there is a need for a piezoelectric energy harvesting system, which efficiently transmits electrical energy to the storage battery with minimum loss. Moreover, there is a need for a piezoelectric energy harvesting system, which is easily installed with little or no changes made to a vehicle or its components.